In 5e, Blindness is described in the PHB as:
A blinded creature can't see and automatically fails any ability check
that requires sight. Attack rolls against the creature have advantage,
and the creature's attack rolls have disadvantage
Grappling is described as a special Melee attack that requires an ability check (STR vs STR or DEX).
Does defending against a Grapple require sight and thus automatically fail if you are blind?
Best Answer
Real life examples provide a good reason to allow grappling while blinded
Arguing with your DM is usually frowned upon. That being said, there's only Run-Fu amongst the martial arts, which I'd personally prefer to grappling in darkness; and I've quite a lot of experience in a variety of martial arts (Karate, Kickboxing, MMA, Brazilian Jujitsu and normal Western boxing plus what you learn growing up in a courtyard of 50 kids and a lot of sticks). Hence, I'd be unhappy with a DM auto-failing grapple checks on blinded opponents. I'd even invite him to test it on me.
Grapple practitioners (greek wrestling, (Brazilian) jujitsu etc.) often practice and even fight at times with their eyes close. The sense of touch (tactility) is way more important when grappling.
Professional blind grappling athletes compete with sighted opponents... and win!
There's substantial professional proof for the claim as shown by the inspirational case of Russel Redenbaugh, a jiu jitsu black belt and serial medal winner (against sighted opponents): https://youtu.be/3xty8T2L7VM and https://en.wikipedia.org/wiki/Russell_Redenbaugh